BIG PHYSICS, BIG QUESTIONS –

Technology : Loud ads could be out on their ear

IT took over 35 years of complaints, but Britain’s TV stations are
finally installing the technology that will show definitively whether TV
advertisements really are louder than programmes.

Unless the volume control on your TV set is broken commercials should be no
louder than the programmes before and after them. But for years, canny
advertisers have been making commercials catch your attention by exploiting the
fact that the apparent loudness of a sound depends on its frequency as well as
its intensity.

Advertisers began playing around with frequencies shortly after the launch of
commercial TV in 1955. By 1960 viewers were complaining that the ad breaks
sounded louder than programmes. The problem worsened when ad makers started
using compressors and filters to ensure that their message would be heard.

Compressors limit the natural peaks in music and speech, while at the same
time boosting the intensity of quieter passages. This makes a sound appear
consistently loud. Another technique, pioneered in the 1960s by the Tamla Motown
studios in Detroit, uses both filters and compressors to separate the audible
spectrum into narrow bands and pack as much energy into each one as possible.
This equalises the level of loudness for all the backing instruments. The voice
of one singer is then mixed to peak at a carefully chosen frequency so it stands
out.

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Compression and filtering makes commercials sound very loud, especially when
broadcast after a sedate black-and-white movie or a quiet nature programme.
Existing sound level meters measure only the energy peaks and cannot pick out
loudness.

The evidence that viewers perceive advertisements as louder is well
established. In 1993 the Broadcasters’ Audience Research Board questioned 3000
viewers and reported that “substantial proportions of viewers” thought that
commercials were too loud.

Then, two years ago, John Emmett, research and development manager of Pearson
Television (and formerly of Thames TV), was given £5000 by the Independent
Television Commission to make a loudness meter.

To get an idea of the relationship between apparent loudness and the peaks in
a soundtrack, Emmett played test tapes of commercials to 40 families, asking
them to grade the sound from quiet to loud. The formula worked out from these
results relates the loudness of sound heard on the TV to the electrical energy
in the signal leaving the broadcaster. Pearson then made a few sample meters and
asked other broadcasters to test them.

The final design is now being manufactured by British electronics company
Michael Stevens and Partners. It costs £2475 and sits between the sound
mixing desk in the TV studio and a TV screen used by engineers to monitor
picture quality. The meter superimposes two bars over the TV picture. One bar
displays the electrical peak level of the signal, measured in decibels, while
the other shows a loudness scale in arbitrary L numbers. The scale reflects the
relative loudness of programmes based on the responses of the test
subjects.

Channel 4 has bought the first 11 production models and the BBC and ITV are
evaluating the next batch.

Broadcast regulations impose a limit on peak sound levels to prevent
overloading of transmitters or receivers. There is no loudness rule, so Channel
4 engineers are now establishing a value that viewers find acceptable.